ABB Industrial IT enabled REX 521 Technical Reference Manual, General page 13

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Technical Reference Manual, General
When starting again, the relay display shows the text
WARNING EEPROM -> FLASH
on the display. This means that the calibration parameters have been read from the
MIM card and copied to the non-volatile memory of the CPU card. After ten
seconds, the relay will reset itself again, and takes the correct calibration parameters
into use.
The unnecessary restoring of factory settings should be avoided because
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all the parameter settings that are written earlier to the relay will be lost,
that is, overwritten with the default values. During normal use this can
cause a protection function to trip when the settings are suddenly changed.
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The protection relay is equipped with a non-volatile memory for preserving
important data during auxiliary supply breaks. For example, when a setting value is
changed, the new value is stored in the memory at the moment of sending it to the
relay, without additional store commands. The memory does not need batteries, and
a lifelong service is guaranteed.
Following data is stored in the non-volatile memory:
• Setting values
• Display state
• Lockout state
1
• Recorded values
• Last 50 events
When the relay is restarted, the same LED indication and text as before the auxiliary
supply break are restored on the display. More information about the alarm LEDs
can be found in chapter "Alarm LEDs" on page 34.
Recorded values are stored from start, trip and other important events. After an
auxiliary power break, time and date and fault currents for the three last events can
be viewed by navigating to the "Recorded values" section of the function block that
caused an indication.
The last 50 events that occurred before the auxiliary power supply break can be
viewed in the HMI event buffer. Time and date for the events are also restored.
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The real-time clock (RTC) is used for time stamping of events. It is also running
during auxiliary power breaks. When the supply is re-established, the relay sets the
right time and new events are stamped accordingly.
The protection relay is provided with a 1-week capacitor back-up protection
enables the internal clock to keep time in case of an auxiliary power failure.
1. Because the storing of the recorded values is a background task, it might be affected
by a sudden auxiliary power failure.
2. Capacitor ageing may decrease the back-up time.
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